1. Field of Invention
This invention relates in general to vehicle HVAC systems, and in particular to window defrost systems.
2. Background of Related Art
Vehicles heating, ventilation, and air conditioning (HVAC) systems provide conditioned air to an interior compartment of a vehicle, and typically include a HVAC module assembly, which has a mixing chamber disposed therein. The mixing chamber combines heated air with cooled air which is output to various ducts and register vents of the vehicle. Examples of the various ducts include vehicle floor ducts, trim panel ducts, and window defrost ducts. A damper within the mixing chamber is positioned to direct the air to either the floor ducts, the trim ducts, the window defrost ducts, or a combination of the ducts depending on the selected mode of operation by a driver or passenger.
When operating the vehicle HVAC system in a floor-only mode position, the damper in the mixing chamber is left partially open to allow air to bleed from the mixing chamber directly to the window defrost duct. This maintains a low flow of conditioned air directed at the windows even though defrost is not selected; however, noise generated in the mixing chamber propagates from the highly turbulent mixing chamber directly to the window defrost duct where it can be heard by the driver and passengers of the vehicle. Such noise is not typically an issue when the window defrost mode is selected since the full thrust of forced air departing the window defrost duct masks the noise of the mixing chamber, but when floor-only mode is selected and the damper is left partially open, the result is unsatisfactory noise propagating through the opening to the window defrost duct and then to the passenger compartment.